It was discovered in the Applicant's laboratory that a pheromone is carried in the feces of the maternally-behaving female rat, a pheromone to which her young are strongly attracted. A series of experiments have been designed: a) to characterize some of the physiological determinants underlying pheromonal emission; b) to determine whether or not response to the pheromone on the part of the young serves an adaptive function; and c) to show how mother and pups reciprocally influence each other to form a "pheromonal bond" during the pre-weaning period.